Chlorination of furan



Patented June 15, 1948 CHLORINATION or FURAN Oliver W. Case and Harry .B. Copelin, Niagara Falls, N. Y., assignors to E. I. du Pont de Nemonrs & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application May 12, 1945, Serial No. 593,532

6 Claims. 101.260-345) I The object of this invention is the preparation of 2-chlorofuran by a new and improved procedure. A still further object of this invention is to prepare this compound by a chlorination procedure which is commercially feasible due to its simplicity and ease of operation. Still further objects will be hereinafter, apparent.

It has hitherto before been thought impossible to directly chiorinate iuran because of the extreme sensitivity of furan to the presence oi small quantities of hydrogen chloride. These traces of hydrogen chloride caused extremely vigorous exothermic polymerization oi furan resulting in the formation of large amounts of black polymeric material. 2-Chlorofuran has previously been prepared by the decomposition of the corresponding chlorinated furoic acid, a process which is economically unattractive. (J. A. C. S. 52:2083.)

We have now found that by careful observation of certain reaction conditions it is possible to chlorinate furan directly to produce 2-chlorofuran in good yield. The tendency of turan to polymerize when in contact with the hydrogen chloride which is secured as a by-product from the above chlorination is avoided by operating under conditions resulting in the almost instan taneous removal of substantially all of the hydrogen chloride from the reaction system. When the polymerization oi furan is thus prevented, a smooth chlorination oi iuran t the chloroiuran becomes possible. The invention is illustrated by the following example:

Example Furan is charged into a reaction vessel which is fitted with a fractionation column containing a lower short packed section. At the top of the packed section of this column an inlet tube for chlorine is provided. At the top of the fractionation column a condenser and receiver is provided. From the receiver the liquid condensate returns through a liquid seal into the re- 2 is present by" the time the furan vapors reach the top of the column. As the monochloroturan which is formed boils at a considerably higher temperature than the iuran, a portion of the monochloride will drop back into the packed section of the column and return to the reaction vessel. The unchlorinated iuran together with a portion of the monochloride and the by-product, hydrogen chloride, will pass into the condenser and receiver. The hydrogen chloride then will be separated in the receiver and passedto theabsorption system while the fur-an together with the monochloride 'will be retumedto the reaction vessel. In this fashion a high concentration of hydrogen chloride in the reaction vessel where the temperature is high is avoided, and excessive polymerization of the furan is prevented. As additional amounts of chlorine are added to the reaction system, the boiling point of the contents of the reaction vessel will increase until it approaches monochloroiuran. At this point chlorination is halted, and the contents of the reactor discharged into a still where separation of the unchlorinated iuran from the monochloride is secured. Operating in this fashion, the formation of the higher chlorides of iuran is substantially avoided, and high yields of 2-chlorofuran are secured. The 2-chlororuran thus obtained, after purification by distillation, is a colorless liquid boiling at 77 C. and has a density of 1.189 at 25 C.

The invention is not restricted to the specific method of the above example. Other modifications will be apparent to the skilled chemist, whereby a relatively small amount of chlorine is fed into furan vapor, the resulting 2-chlorofuran is condensed out, and the remaining mixture of iuran vapor and hydrogen chloride is condensed to liqueiy the furan and thus liberate the gaseous HCl. The condensed 2-chlorofuran may be separately collected, if desired, or it may be mixed with the condensed furan, as in the above example.

'Ii desired, the reaction temperature may be maintained above the boiling point of the product, 2-chlorofuran, up to C. Above 100 C. polymerization of iuran becomes excessive. We prefer to maintain the reaction temperature below the boiling point of Z-chloroiuran (77 C.) but above the boiling point of furan (32 C.) e. g., at around 50 C.

The amount of chlorine fed into this iuran vapor must be relatively small and should not exceed the ratio or 0.1 volume or chlorine to one volume of (area. This ratio may be as low as 0.01 to 1 or even lower, if desired.

We claim:

1. The process for the production of 2-chlorofuran which comprises introducing chlorine into a flowing stream of furan vapor maintained at a temperature between the boiling points of iuran and 2-chloroluran in the ratio of not more than about 0.1 volume of chlorine to one volume of iuran, separating condensed 2-chlorofuran from said vapor and separating hydrogen chloride from the remaining vapor by condensing the iuran.

2. The process for the production of 2-chloroutran which comprises introducing chlorine into a flowing stream of furan vapor at a temperature not higher than about 100 C. in the ratio of not more than about 0.1 volume of chlorine to one volume of furan, condensing 2-chloroturan from said vapor, and separating hydrogen chloride from the remaining iuran vapor by condensing said Man vapor.

3. The process for the production of 2-chloroiuran which comprises introducing chlorine into a flowing stream of furan vapor at a temperature not higher than about 100 C. in the ratio of not more than about 0.1 volume of chlorine to one volume 01' furan vapor and separating hydrogen chloride from said vapor by condensing 2-chlorofuran and furan therefrom,

4. The process for the production of 2-chlorofuran which comprises continuously flowing a stream of furan vapor through a space wherein said vapor is maintained at a temperature between the boiling points of furan and 2-chlorofuran, introducing chlorine into said stream of turan vapor in the ratio oi about 0.01 to 0.1 volume of chlorine to one volume or iuran vapo removing condensed z-chloroiuran from said space and separating hydrogen chloride from the vapors flowing from said space by cooling; to condense furan therefrom.

5. The process for the production of z-chlorofuran which comprises passing turan vapor upwardly through a distilling column maintained at a temperature between the boiling points of furan and z-chloroturan, passing chlorine into said column at a ratio of 0.01 to 0.1 volume to one volume of furan vapor. withdrawing condensed 2-chloroi'uran from the lower part of said column and furan vapor and hydrogen chloride from the upper part thereof and condensin the eiliuent iuran vapor so as to separate hydrogen chloride therefrom.

6. The process for the production or 2-chlorofuran which comprises introducing chlorine into a flowing stream of furan vapor at a temperature not higher than about C. in the ratio of not more than about 0.1 volume of chlorine to one volume of furan vapor. and separating hydrogen chloride from said vapor by condensing the iuran and condensing 2-chloroturan from said vapor.

OLIVER W. CASS. HARRY B. COPELIN.

REFERENCES CITED The following references are of record in the file of this patent:

Chemical Abstracts, vol. 24, p. 3011 of 1930.

Unit Processes in Organic Synthesis. by Groggins, 1938, 2d ed., pp. 166, 184, 185. (Copy in Div. 63.) 

